If you have an iPhone 3G running iOS 4, you know how painfully slow your device can be. This is due to the fact that iOS 4 was designed for more powerful devices like the iPhone 3GS and the iPhone 4.
To do so, go to Settings > General >Home Button > Spotlight Search, then turn off everything and reboot your iPhone.
I don’t have an iPhone 3G so I wasn’t able to verify this but looking at all the positive comments over at MMI, I assume this is working like a charm.
Please try it and let us know how it goes for you.